1. Field of the Invention
This invention relates generally to a stereophonic signal demodulator, and is directed more particularly to an FM stereophonic signal demodulator of relatively simple circuit construction wherein a crosstalk component in the respective output signals can be substantially entirely eliminated.
2. Description of the Prior Art
In the prior art, there have been proposed a number of FM stereophonic signal demodulators including crosstalk elimination circuits. In a typical prior art demodulator, left and right channel audio signals are demodulated, respectively, to produce left and right channel signals 2L + .DELTA.R and 2R + .DELTA.L, respectively. The component .DELTA.R represents a crosstalk component of the right channel that is present in the left channel output signal and, similarly, the component .DELTA.L represents a crosstalk component in the right channel output signal. Heretofore, these crosstalk components have been eliminated by adding a portion of the main channel signal (L+R) of the received composite stereo signal to the demodulated signals in reverse phase. If the signal demodulator is of the type which includes switching circuits, then the crosstalk elimination circuit must be specifically designed to reduce carrier leakage which may be produced in the demodulator switching circuit.
Crosstalk may be significantly reduced if a pair of composite stereo signals of opposite phase are derived by a phase division type of amplifier from the composite stereo signals produced by an FM discriminator, and if this pair of signals is supplied to a pair of switching-type demodulators to thereby demodulate signals 2L+.DELTA.R, 2R+.DELTA.L, -(.DELTA.R+.DELTA..DELTA.L) and -(.DELTA.L+.DELTA..DELTA.R), respectively. Then, if corresponding ones of these demodulated signals are added to reduce the crosstalk components .DELTA.R and .DELTA.L, signals 2L-.DELTA..DELTA.L and 2R-.DELTA..DELTA.R are produced. However, this technique requires the use of the phase division type of amplifier, which normally is formed of two transistor amplifiers having a variable resistor connected between the emitter electrodes. This is a rather complicated circuit construction and lowers the S/N ratio of the composite stereo signal because of the amplifier stage.